Single-photon sensitive light-in-fight imaging
The MIT Faculty has made this article openly available. Please share
how this access benefits you. Your story matters.
Citation
Gariepy, Genevieve, Nikola Krstajic, Robert Henderson,
Chunyong Li, Robert R. Thomson, Gerald S. Buller, Barmak
Heshmat, Ramesh Raskar, Jonathan Leach, and Daniele Faccio.
“Single-Photon Sensitive Light-in-Fight Imaging.” Nature
Communications 6 (January 27, 2015): 6021.
As Published
http://dx.doi.org/10.1038/ncomms7021
Publisher
Nature Publishing Group
Version
Final published version
Accessed
Wed May 25 22:40:51 EDT 2016
Citable Link
http://hdl.handle.net/1721.1/96779
Terms of Use
Creative Commons Attribution
Detailed Terms
http://creativecommons.org/licenses/by/4.0/
ARTICLE
Received 18 Aug 2014 | Accepted 2 Dec 2014 | Published 27 Jan 2015 | Updated 25 Feb 2015
DOI: 10.1038/ncomms7021
OPEN
Single-photon sensitive light-in-flight imaging
Genevieve Gariepy1, Nikola Krstajić2,3, Robert Henderson2, Chunyong Li1, Robert R. Thomson1,
Gerald S. Buller1, Barmak Heshmat4, Ramesh Raskar4, Jonathan Leach1 & Daniele Faccio1
The ability to record images with extreme temporal resolution enables a diverse range
of applications, such as fluorescence lifetime imaging, time-of-flight depth imaging and
characterization of ultrafast processes. Recently, ultrafast imaging schemes have emerged,
which require either long acquisition times or raster scanning and have a requirement for
sufficient signal that can only be achieved when light is reflected off an object or diffused
by a strongly scattering medium. Here we present a demonstration of the potential of
single-photon detector arrays for visualization and rapid characterization of events evolving
on picosecond time scales. The single-photon sensitivity, temporal resolution and full-field
imaging capability enables the observation of light-in-flight in air, as well as the measurement
of laser-induced plasma formation and dynamics in its natural environment. The extreme
sensitivity and short acquisition times pave the way for real-time imaging of ultrafast
processes or visualization and tracking of objects hidden from view.
1 Institute of Photonics and Quantum Sciences, Heriot-Watt University, David Brewster Building, Edinburgh EH14 4AS, UK. 2 Institute for Micro and Nano
Systems, University of Edinburgh, Alexander Crum Brown Road, Edinburgh EH9 3FF, UK. 3 Queen’s Medical Research Institute, University of Edinburgh, 47
Little France Crescent, Edinburgh EH16 4TJ, UK. 4 Camera Culture, MIT Media Lab, MIT, 75 Amherst Street, E14-474, Cambridge, Massachusetts 02139,
USA. Correspondence and requests for materials should be addressed to G.G. (email: gg132@hw.ac.uk) or to D.F. (email:d.faccio@hw.ac.uk).
NATURE COMMUNICATIONS | 6:6021 | DOI: 10.1038/ncomms7021 | www.nature.com/naturecommunications
& 2015 Macmillan Publishers Limited. All rights reserved.
1
ARTICLE
NATURE COMMUNICATIONS | DOI: 10.1038/ncomms7021
L
ight was first captured in its flight by Abramson in 1978
(ref. 1), who used a holographic technique to record the
wavefront of a pulse propagating and being scattered by a
white-painted screen placed in its path. This high-speed recording
technique allowed the dynamic observation of light phenomena
like reflection, interference and focusing that are normally
observed statically2,3. More recently, light-in-flight holography
has been performed in a scattering medium rather than using a
reflective screen4,5. Light can also be captured in motion in a
scattering medium using a streak camera that has picosecond
temporal resolution, thus removing the need for interferometry
and coherent illumination but requires additional hardware to
raster scan the two-dimensional (2D) scene, which increases the
acquisition time to hours6,7. A few other techniques possess the
temporal resolution to observe light in motion as it illuminates a
scene, such as photonic mixer devices based on modulated
illumination, albeit with a temporal resolution limited to a few
nanoseconds8. Alternatively, time-encoded amplified imaging can
record images at the repetition rate of a laser by exploiting
wavelength-encoded illumination of a scene and amplified
detection through a dispersive fibre, albeit with 160 ns temporal
and spatial resolution9. Recent studies based on computer
tomography using data from multiple probe pulses enabled
reconstruction of picosecond pulse propagation phenomena in
condensed media10. The current challenge is to simplify data
acquisition and reduce acquisition times by achieving full imaging
capability and low-light sensitivity while maintaining temporal
resolution in the picosecond regime.
Here we address this challenge and provide an imaging solution
that simultaneously acquires spatial and temporal information
(x, y and t). The technology we use is based upon a
two-dimensional Silicon CMOS array of single-photon
avalanche diode (SPAD) detectors with each individual pixel
operated in time-correlated single-photon counting (TCSPC)
mode11–14. Individual SPAD detectors are increasingly used
throughout the field of optics; in particular, their high temporal
resolution has made them useful for single-photon time-of-flight
measurements15,16, fluorescence lifetime imaging14 and photon
counting17. Recent advances in electronics have enabled the
development of arrays of SPADs, giving the capability to perform
light-in-flight measurements. In these experiments, we use a
32 32-pixel array that has single-photon sensitivity and acquires
time information with a resolution of 67 ps, which provides the
ability to freeze the motion of light with a blurring of only a few
centimeters18.
Results
Experimental setup. The setup for our experiment is illustrated
in Fig. 1. The scene is imaged onto the SPAD array using a fisheye
lens. Laser pulses propagate at 4 kHz from right to left across the
field of view and are reflected by two mirrors. Light from the laser
pulses is scattered by air molecules and then detected by the
SPAD camera.
The SPAD camera is operated in TCSPC mode: every pixel has
its own picosecond timer. The timer is started by the detection of
a
ew
f vi
o
ield
F
Laser
Ligh
t-in-
fligh
and tr
igger
t sce
ne
SPA
D ca
b
Histogram
mer
a
)
pixel (22,21
Counts
y
Integrated
SPAD imag
e
y
EMCCD
image
y
Time
4n
s
2n
3n
s
x
s
x
1n
s
0n
s
Figure 1 | Light-in-flight measurement and data cube. (a) A laser pulse is reflecting off multiple mirrors, passing three times across the field of view of the
SPAD camera (35 35 cm2). The same laser is used to create a trigger sent to the camera. The SPAD camera collects scattered photons from the
laser pulse. The field of view does not contain the mirrors because the scattered light coming from the mirror surfaces is much more intense than the
Rayleigh-scattered light during propagation. (b) The histogram indicates the time of arrival of the laser pulse as measured by pixel (22, 21). The time
frames, shown at 0, 1, 2, 3 and 4 ns, show the evolution of the pulse in time as it propagates across the scene. The integration of all frames gives the total
path followed by the light, similarly to what can be acquired by an EMCCD camera at maximum gain for an exposure time of 7 s.
2
NATURE COMMUNICATIONS | 6:6021 | DOI: 10.1038/ncomms7021 | www.nature.com/naturecommunications
& 2015 Macmillan Publishers Limited. All rights reserved.
ARTICLE
NATURE COMMUNICATIONS | DOI: 10.1038/ncomms7021
Raw image
Light propagation in air. The final result is shown in Fig. 3
where we show the evolution of the light pulse propagating
through air. The figure shows selected time frames acquired by
the camera, each separated by 0.7 ns and overlaid on a photograph (taken with a commercial DSLR camera) of the setup. The
field of view of the SPAD camera is represented by dashed lines
on each frame. In the first frame, the laser pulse has just entered
the field of view. We then see the pulse propagate and reflecting
Background subtracted image
Counts
60
40
20
0
0
2
4
6
0
2
4
6
0
2
4
Time (ns)
6
2
4
6
0
2
4
6
0
2
4
6
60
40
20
0
60
40
20
0
Interpolated image
Time histograms
De-noised image
Gaussian fitting
Data processing. The unique features of the three-dimensional
data allow efficient data processing and noise suppression in both
the temporal and spatial dimensions. The image processing
algorithm is schematically illustrated in Fig. 2 that shows the timeintegrated image after each step of the data processing. Starting
with the raw data, we first subtract the background data cube
acquired in the same conditions, but without the laser propagating
through the scene. Second, every time histogram is fitted with a
Gaussian. For pixels containing signal from the laser pulse, this
fitting removes what we could call the ‘temporal noise’, that is, the
noise in the time bins with no signal from the laser pulse.
Moreover, some spatial pixels are never illuminated by the laser
pulse scatterings and contain only noise and background light and
are thus set to zero. We therefore use the time information contained in each pixel to improve the spatial quality of our data.
Third, we deconvolve the instrument impulse response function
(largely due to electronic jitter and measured by uniformly illuminating the camera with a 100-fs laser pulse) from the Gaussian
fits. This results in histograms with a full-width at half-maximum
of B500 ps FWHM that is consistent with an independent
measurement of the laser pulse duration. Finally, we increase the
spatial quality of the images by a standard linear re-interpolation,
frame by frame, between each line and column of the 32 32 pixel
array as in Fig. 2. We interpolate in a way that connects the centre
of mass of each line and column, in order to achieve a final spatial
310 310 pixel count. Summarizing, the data processing essentially relies on a three-stage process composed of noise removal,
temporal deconvolution and re-interpolation: this process does
not require any a priori knowledge of the scene content itself and
is therefore inherently robust. The re-interpolation process is a
very basic nearest-neighbour interpolation: no information is lost
in this process and, naturally, no information is gained either.
More importantly, all quantitative data analysis (for example, the
plasma decay times as discussed below), is always performed on
the raw (not interpolated) data.
Counts
60
40
20
0
0
60
40
20
0
Deconvolution
a single photon, and stopped by the arrival of a periodic trigger,
which is derived from the laser pulses. The time between start and
stop is recorded, and a histogram of photon arrival times builds
up as a number of optical pulses successively propagate through
the setup. The camera is connected directly to a computer and we
acquire data for the histograms during a 10-min period—this
corresponds to 2 million identical pulses propagating through the
setup. Use of a higher repetition rate laser (MHz) would result in
the acquisition time being reduced to less than 1 s.
Figure 1 gives a schematic representation of the data cube (x, y
and t) acquired by the SPAD array. The histogram in Fig. 1 shows
a 5-ns section for one of the pixels in the array: considering all of
the x, y locations at one particular time t gives a snapshot of the
spatial position of the laser pulse as shown for example in the
individual time frames in Fig. 1. Integrating all time frames gives
a static representation of the path followed by the light, similar to
what is captured with an EMCCD camera, also shown in Fig. 1.
60
40
20
0
Time (ns)
Figure 2 | Data processing. (a) To process the acquired data, we first subtract a background acquired by the SPAD camera without the laser beam
propagating across its field of view. It allows us to see the path, but the image (b) is still very noisy. (c) To get a clearer image, we fit a Gaussian to every
histogram. If the Gaussian is much wider than we expect, or smaller than the pulse duration, we set the histogram to zero. (d) We then deconvolve
the fitted Gaussians down to a 500-ps Gaussian (e). (f) Finally, to improve the resolution of our frames, we interpolate between the centre of mass of two
adjacent lines/columns.
NATURE COMMUNICATIONS | 6:6021 | DOI: 10.1038/ncomms7021 | www.nature.com/naturecommunications
& 2015 Macmillan Publishers Limited. All rights reserved.
3
ARTICLE
NATURE COMMUNICATIONS | DOI: 10.1038/ncomms7021
Integrated image
1.2 ns
1.9 ns
2.6 ns
3.3 ns
4 ns
4.7 ns
Time frames
Figure 3 | Frames of the light-in-flight movie. In these frames, we see a pulse of light propagating between three mirrors. The laser first hits the mirror on
the right and is directed towards the field of view of the SPAD camera, as indicated by the green arrow on the integrated image. The FOV is represented by
dashed rectangles and corresponds to a 35 35 cm2 region. In the first and second frames, we show the laser pulse entering the FOV. In the second, third
and fourth frames, we see the light being reflected by the mirrors, before exiting the FOV in the last frame.
off the two mirrors in the subsequent frames, before finally
leaving the field of view. A video of the full evolution of the
laser pulse propagation is provided as Supplementary Video 1.
The scene that we observed, that is, the pulse reflecting between
the three mirrors, happens within a few nanoseconds, only a
fraction of the 69 ns time range of the camera. During that time,
the 500 ps pulse, which is 15-cm long, travels 67 ps or 2 cm
between each frame of the movie. The figure (and video) clearly
demonstrates that we are able to capture the full dynamic of light
propagation in air.
In these measurements, the average count rate from the
detector is found to be of the order of 0.0005 detected events per
laser pulse, per pixel. Even allowing for the relatively low fillfactor and single-photon detection efficiency, this implies a
photon flux of the order of 0.2 photons per pulse, per full pixel
area. The combination of single-photon sensitivity and picosecond temporal resolution make it very difficult for detector
technologies such as intensified CCD19 to achieve the results
shown.
Plasma dynamics. We also captured the dynamics of a more
complex light phenomenon that is still the object of intense
research studies for various applications: the formation of a
weakly ionized plasma filament by a femtosecond laser pulse20.
Laser pulses with 90 fs, 12 mJ (Amplitude Technologies), 785 nm
wavelength at a 100-Hz repetition rate were loosely focused with
a 50-cm lens to create a weak and tenuous plasma filament
approximately 5 cm long, in the field of view of the SPAD camera.
The weakly ionized plasma filament emits a faint fluorescence
signal, largely in the 300–440 nm wavelength range21. The data
were acquired for 2 min in two different spectral ranges using
4
coloured filters: in red, to isolate the propagation of the laser
pulse, and in blue, to isolate the plasma fluorescence. Figure 4
shows the scene for selected time frames (a full video is available
as Supplementary Video 2). We first observe the femtosecond
pulse (red) coming into the field of view and becoming brighter in
the second frame as the pulse is scattered by the plasma created
by its leading edge. The beam then moves out of the field of view,
with a reduced intensity because of scattering from the selfinduced plasma. We can also see the plasma (blue) being formed
and still fluorescing well after the beam has passed. The time
histograms (an example is also shown in Fig. 4) reveal an
exponential decay with a lifetime of approximately 600 ps,
consistent with previous measurements20. It is important to
note that the technique described here allows to characterize the
plasma dynamics without the need to introduce any additional
scattering agents, which would severely alter the plasma
formation process itself.
Discussion
Our measurements open new possibilities for measuring ultrafast
temporal dynamics within extremely low-intensity events.
Remarkably, we are now able to observe light-in-flight at the
sub-nanosecond scale in air where scattering occurs only from the
ambient gas molecules. We underline that the SPAD camera not
only allows to record a scene dynamically on very short-time
scales, but it also provides an additional opportunity for noise
reduction by exploiting the temporal dimension. Other applications are viable where the ability to record low photon numbers
with high temporal resolution will enable viewing objects that are
hidden from view, for example, looking around corners22–24 or
through walls24–26. The single-photon sensitivity of our ultrafast
NATURE COMMUNICATIONS | 6:6021 | DOI: 10.1038/ncomms7021 | www.nature.com/naturecommunications
& 2015 Macmillan Publishers Limited. All rights reserved.
ARTICLE
Time
Norm. counts
5.0 ns
4.0 ns
3.4 ns
3.1 ns
2.5 ns
1.7 ns
NATURE COMMUNICATIONS | DOI: 10.1038/ncomms7021
1
0.8
0.6
0.4
0.2
0
0
2
4
6
8
Time (ns)
10
Figure 4 | Plasma evolution recorded by light-in-flight. (a) In these
frames, the femtosecond pulse is shown in red, and the plasma
fluorescence in blue. The plasma is created as soon as the leading edge of
the pulse passes through focus. The laser pulse is then scattered by the
plasma, which can be seen in the second frame. As a large portion of the
beam is scattered or absorbed at the focus by the plasma, the exiting beam
is weaker, as we observe in the third to fifth frames. We also see the plasma
being formed at focus when the laser pulse is focused, then evolving and
decaying after the pulse has passed. A full video is provided as
Supplementary Video 2. (b) The graph shows the temporal histogram of the
plasma fluorescence (solid black curve, normalized photon counts, raw
data) corresponding to the region indicated with a white square in the last
frame. The dashed line is the detector impulse response function, the
dotted red curve is an exponential decay fit with a 600-ps decay constant.
imaging method enables direct spatially resolved measurements
of dynamic quantum phenomena19, and also very weak scattering
phenomena such as air-born acousto-optic effects27.
Methods
Details of experimental setup. The fisheye lens of 12-mm focal length provides a
35-cm wide field of view at the chosen object distance of 1.8 m. The laser used to
observe light reflecting off mirrors is a 532-nm wavelength microchip laser (Teem
Photonics STG 03E), which emits 500 ps duration pulses of 3.5 mJ energy at 4 kHz
repetition rate. The laser polarization is set to vertical to maximize scattering in the
direction of the camera. Experiments repeated in a pure nitrogen environment
(data not shown) gave identical light intensities on the camera, thus verifying that
the scattering is from air molecules and not from any possible dust particles that
may be present in a standard atmospheric environment.
5. Kubota, T., Komai, K., Yamagiwa, M. & Awatsuji, Y. Moving picture recording
and observation of three-dimensional image of femtosecond light pulse
propagation. Opt. Express 15, 14348–14354 (2007).
6. Velten, A. et al. Femto-photography: capturing and visualizing the propagation
of light. ACM Trans. Graph 32, 44:1–44:8 (2013).
7. Velten, A., Lawson, E., Bardagjy, A., Bawendi, M. & Raskar, R. Slow art with a
trillion frames per second camera. Proc. SIGGRAPH 44 (2011).
8. Heide, F., Hullin, M. B., Gregson, J. & Heidrich, W. Low-budget transient
imaging using photonic mixer devices. ACM Trans. Graph 32, 45:1–45:10
(2013).
9. Goda, K., Tsia, K. & Jalali, B. Serial time-encoded amplified imaging for realtime observation of fast dynamic phenomena. Nature 458, 1145–1149 (2009).
10. Li, Z., Zgadzaj, R., Wang, X., Chang, Y.-Y. & Downer, M. C. Single-shot
tomographic movies of evolving light-velocity objects. Nat. Commun. 5, 3085
(2014).
11. O’Connor, D. & Phillips, D. Time-Correlated Single Photon Counting
(Academic, 1984).
12. Becker, W. Advanced Time-Correlated Single Photon Counting Techniques
Vol. 81 (Springer, 2005).
13. Richardson, J. et al.A 32 32 50ps resolution 10 bit time to digital converter
array in 130nm cmos for time correlated imaging. Custom Integrated Circuits
Conference, 2009. IEEE CICC ’09, 77–80 (2009).
14. Li, D.-U. et al. Real-time fluorescence lifetime imaging system with a 32 32
cmos low dark-count single-photon avalanche diode array. Opt. Express 18,
10257–10269 (2010).
15. Buller, G. S. & Wallace, A. Ranging and three-dimensional imaging using timecorrelated single-photon counting and point-by-point acquisition. IEEE J. Sel.
Top. Quantum Electron. 13, 1006–1015 (2007).
16. Kirmani, A. et al. First-photon imaging. Science 343, 58–61 (2014).
17. Guerrieri, F., Tisa, S., Tosi, A. & Zappa, F. Two-dimensional spad imaging
camera for photon counting. IEEE Photon. J. 2, 759 (2010).
18. Richardson, J., Grant, L. & Henderson, R. Low dark count single-photon
avalanche diode structure compatible with standard nanometer scale cmos
technology. IEEE Photon. Technol. Lett. 21, 1020–1022 (2009).
19. Fickler, R., Krenn, M., Lapkiewicz, R., Ramelow, S. & Zeilinger, A. Real-time
imaging of quantum entanglement. Sci. Rep. 3, 1914 (2013).
20. Couairon, A. & Mysyrowicz, A. Femtosecond filamentation in transparent
media. Phys. Rep. 441, 47–189 (2007).
21. Xu, H., Azarm, A., Bernhardt, J., Kamali, Y. & Chin, S. The mechanism of
nitrogen fluorescence inside a femtosecond laser filament in air. Chem. Phys.
360, 171 (2009).
22. Velten, A. et al. Recovering three-dimensional shape around a corner using
ultrafast time-of-flight imaging. Nat. Commun. 3, 745 (2012).
23. Gupta, O., Willwacher, T., Velten, A., Veeraraghavan, A. & Raskar, R.
Reconstruction of hidden 3d shapes using diffuse reflections. Opt. Express 20,
19096–19108 (2012).
24. Katz, O., Small, E. & Silberberg, Y. Looking around corners and through thin
turbid layers in real time with scattered incoherent light. Nat. Photon. 6,
459–553 (2012).
25. Freund, I. Looking through walls and around corners. Phys. A Stat. Mech. Appl.
168, 49–65 (1990).
26. Popoff, S., Lerosey, G., Fink, M., Boccara, A. C. & Gigan, S. Image transmission
through an opaque material. Nat. Commun. 1, 81 (2010).
27. Heshmat, B. et al. The effect of detector distance and beam width in acoustooptical beam deflection probing in air. J. Opt. L. Tech. 44, 734 (2012).
Acknowledgements
Time-correlated single-photon counting. The TCSPC timer of the SPAD array is
operated in reverse mode, that is, it is started by the detection of a single photon,
and stopped by the arrival of a periodic trigger. The trigger is derived from detection
of a reflection of the laser pulse with an optical constant fraction discriminator
(Becker & Hickl OCF-401). The time range of the histogram acquired in TCSCP
mode is 68.6 ns with a bin-width of 67 ps (determined by the 10 bit acquisition
electronics), and the median dark count rate of the pixels is 50 counts per second. In
the experiment, the SPAD camera detects an average of 0.0005 photon per pulse per
pixel, thus operating in the photon-starved regime as required for TCSPC.
We acknowledge support from the European Research Council under the European
Union’s Seventh Framework Programme (FP/2007-2013)/ERC GA 306559, the Engineering and Physical Sciences Research Council (EPSRC, UK, Grants EP/J00443X/1, EP/
K03197X/1, EP/K015338), UK-STFC (grant ST/H005595/1), USAR Laboratory and
USAR Office through the ISN (contract number W9911NF-13-D-0001) and ST
Microelectronics, Imaging Division, Edinburgh, for their support in the manufacture of
the Megaframe chip. The Megaframe project has been supported by the European
Community within the Sixth Framework Programme IST FET Open.
Author contributions
References
1. Abramson, N. Light-in-flight recording by holography. Opt. Lett. 3, 121–123
(1978).
2. Abramson, N. Light-in-flight recording: high-speed holographic motion
pictures of ultrafast phenomena. Appl. Opt. 22, 215–232 (1983).
3. Abramson, N. H. & Spears, K. G. Single pulse light-in-flight recording by
holography. Appl. Opt. 28, 1834–1841 (1989).
4. Häusler, G., Herrmann, J. M., Kummer, R. & Lindner, M. W. Observation of
light propagation in volume scatterers with 1011-fold slow motion. Opt. Lett.
21, 1087–1089 (1996).
G.G. performed the experiments and drafted the manuscript. R.H. designed the CMOS
SPAD pixel architecture, N.K. provided support with CMOS SPAD array, C.L. and J.L.
assisted with the experiments, R.R.T. and D.F. conceived the light-in-flight imaging work
using the SPAD array camera. D.F. supervised and directed the project. All authors
contributed to scientific discussions and to the final manuscript.
Additional information
Supplementary Information accompanies this paper at http://www.nature.com/
naturecommunications
NATURE COMMUNICATIONS | 6:6021 | DOI: 10.1038/ncomms7021 | www.nature.com/naturecommunications
& 2015 Macmillan Publishers Limited. All rights reserved.
5
ARTICLE
NATURE COMMUNICATIONS | DOI: 10.1038/ncomms7021
Competing financial interests: The authors declare no competing financial interests.
Reprints and permission information is available online at http://npg.nature.com/
reprintsandpermissions/
How to cite this article: Gariepy, G. et al. Single-photon sensitive light-in-flight imaging.
Nat. Commun. 6:6021 doi: 10.1038/ncomms7021 (2015).
6
This work is licensed under a Creative Commons Attribution 4.0
International License. The images or other third party material in this
article are included in the article’s Creative Commons license, unless indicated otherwise
in the credit line; if the material is not included under the Creative Commons license,
users will need to obtain permission from the license holder to reproduce the material.
To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/
NATURE COMMUNICATIONS | 6:6021 | DOI: 10.1038/ncomms7021 | www.nature.com/naturecommunications
& 2015 Macmillan Publishers Limited. All rights reserved.
DOI: 10.1038/ncomms7408
Erratum: Single-photon sensitive light-in-flight
imaging
Genevieve Gariepy, Nikola Krstajić, Robert Henderson, Chunyong Li, Robert R. Thomson, Gerald S. Buller,
Barmak Heshmat, Ramesh Raskar, Jonathan Leach & Daniele Faccio
Nature Communications 6:6021 doi: 10.1038/ncomms7021 (2015); Published 27 Jan 2015; Updated 25 Feb 2015
The original version of this Article contained a typographical error in the spelling of ‘flight’ in the title of the paper. This has now been
corrected in both the PDF and HTML version of the Article.
NATURE COMMUNICATIONS | 6:6408 | DOI: 10.1038/ncomms7408 | www.nature.com/naturecommunications
& 2015 Macmillan Publishers Limited. All rights reserved.
1